Microtomes

ABSTRACT

A sledge microtome of the kind in which the specimen holder is raised stepwise at the beginning of each cutting stroke by means of a ratchet and pawl mechanism is provided with a device to slow down the rate of rotation of the ratchet in the last few degrees of its rotation to prevent it over-running its desired end position under its own momentum. In one form, the device consists of an auxiliary lever pivoted at one end of a main lever carrying the pawl and arranged to engage a trip which initially rotates the two levers together, and stops arranged to engage the levers in such a manner that, over the last few degrees of rotation, the auxiliary lever rotates relative to the main lever and thereby slows down the rotation of the main lever.

United States Patent 1 1 1111 3,872,759

Jackson 1 Mar. 25, 1975 [54] MICROTOMES 3,757,591 9/1973 Taylor.... 74/4241; A

[ Inventor: Brian Laurence J Histon, 3,771,405 11/1973 Blum 83/714 England Primary Examiner-Donald R. Schran [73] Assignee: Kent Cambridge Medical Limited, Attorney, Agent, or Firm--Browdy and Neimark [22] Filed: Mar. 8, 1974 [2]] Appl. No.: 449,480

[30] Foreign Application Priority Data Mar. 12,1973 unigeq gn q 11793/73 [52] US. Cl 83/718, 83/9l5.5,'83/414, 83/522, 83/727, 83/729, 83/714 [51] Int. Cl. G0ln 1/06 [58] Field of Search 83/414, 707, 714, 717, 83/718, 729, 727, 915.5, 522

[56] References Cited UNITED STATES PATENTS Cambridge, England 2/1970 Blum 83/414 X [57] ABSTRACT A sledge microtome of the kind in which the specimen holder is raised stepwise at the beginning of each cutting stroke by means of a ratchet and pawl mechanism is provided with a device to slow down the rate of rotation of the ratchet in the last few degrees of its rotation to prevent it over-running its desired end position under its own momentum. In one form, the device consists of an auxiliary lever pivoted at one end of a main lever carrying the pawl and arranged to engage a trip which initially rotates the two levers together. and stops arranged to engage the levers in such a manner that, over the last few degrees of rotation, the auxiliary lever rotates relative to the main lever and thereby slows down the rotation of the main lever.

10 Claims, 8 Drawing Figures WTENTED SHLU 2 OF 6 F/GZ PATENTEWZS'QTS 3.872.759

sum 5 or e 1 MHCROTOMES This invention relates to microtomes.

More particularly, the invention relates to microtomes of the kind comprising a first member carrying a knife and a second member carrying a specimen holder, the first and second members being relatively movable in a straight line to enable a layer of preselected thickness to be cut by the knife from a specimen held by the specimen holder, and a ratchet and pawl mechanism for automatically decreasing by a preset amount, after each cutting operation, the separation, measured in the direction perpendicular to the direction of relative movement of the members, between the knife and the specimen holder.

In known microtomes, the ratchet and pawl mechanism consists of a ratchet wheel rotatably mounted on the second member and arranged so that rotation of the ratchet wheel in one sense through a pre-set angle produces a correspondingly pre-set movement of the specimen holder towards the knife, a lever pivotally mounted on the second member and carrying a pawl which engages the ratchet wheel during pivotal movement of the lever in one sense to effect rotation of the ratchet wheel, a trip element mounted on the first member so as to engage the lever during relative movement of the members in one direction thereby to cause rotation of the lever in the said sense, and a stop element on the second member positioned to stop at a predetermined point the rotation of the lever by the trip element. It has been found that, with such an arrangement, the inertia of the ratchet wheel tends to cause it to continue rotating after rotation of the lever has been halted by the stop element, so that the specimen holder is moved beyond the predetermined position required for it to give the desired specimen thickness on the succeeding cutting operation.

According to this invention there is provided a mi crotome of the kind set forth, in which the ratchet and pawl mechanism comprises a ratchet wheel rotatably mounted on one of the relatively movable members and arranged so that rotation of the ratchet wheel in one sense through a pre-set angle effects a correspondingly pre-set decrease in the separation between the knife and specimen holder, a lever assembly pivotally mounted on the same member and carrying a pawl which engages the ratchet wheel during pivotal movement of the lever assembly in one sense to effect rotation in the said sense of the ratchet wheel, a trip element mounted on the other of the relatively movable members so as to engage the lever assembly during relative movement of the members in one direction thereby to cause rotation of the lever assembly in the said sense, a stop element mounted on the firstmentioned one of the relatively movable members and positioned to engage the lever assembly to stop, at a predetermined point, rotation thereof by the trip element, the lever assembly including means for reducing, during part of the rotation of the lever assembly immediately before its engagement with the stop element, the speed of rotation of the ratchet wheel effected by a given speed of relative movement between the relatively movable members.

Preferably, the lever assembly comprises a main lever carrying the pawl, and an auxiliary lever pivotally mounted on the main lever for rotation about an axis parallel to and spaced from the pivotal axis of the main lever and positioned so as to be engaged by the trip element, at a point on one side of its pivotal axis, resilient biasing means connected between the main and auxiliary levers to urge the main lever to follow the rotation of the auxiliary lever when it is engaged by the trip element, and a second stop element positioned to engage the auxiliary lever, at a point on the side of its pivot axis opposite its point of contact with the trip element, before the main lever engages the first-mentioned stop element, so that, during part of the rotation of the lever assembly immediately before engagement of the main lever with the first stop element, the auxiliary lever rotates relative to the main lever against the resilience of the biasing means thereby to reduce the speed of rotation of the main lever effected by a given speed of relative movement between the relatively movable members.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a sledge microtome constructed in accordance with the invention;

FIG. 2 is an end elevation of the sledge of the microtome of FIG. 1, looking in the direction of arrow [I in FIG. 1;

FIG. 3 is a side elevation, partly in section on line III- III of FIG. 2, of the sledge with specimen holder omitted for the sake of clarity;

FIG. 4 is a cross-section on line IV-IV of FIG. 3, showing also a fragment of one side wall of the base casting in which the sledge moves and the trip assembly fixed to the wall;

FIG. 5 is an underneath plan view of the sledge, partly in section on line V-V of FIG. 4, and of the trip assembly;

FIG. 6 is a fragmentary underneath plan view of part of the sledge; and

FIGS. 7A and 7B are diagrammatic underneath plan views of part of a ratchet and pawl mechanism of the sledge, showing the mechanism at two successive stages in its operation.

The sledge microtome shown in the drawings is similar apart from the ratchet and pawl mechanism de scribed in detail below, to the microtome described in US. Pat. No. 3,757,591.

The sledge microtome shown in the drawings comprises a box-like base casting 10, consisting of end walls 12 and 14 and side walls 16 and lid which support horizontal rails 20, and a sledge 22 slidable on the rails 20. Near one of its ends the base casting 10 carries a knife 24 mounted in knife supports 26 by means of which the angle of cut and the orientation of the blade can be adjusted whilst the cutting edge of the blade is maintained in a horizontal plane above the level of the rails 20. The sledge 22 comprises an upper wall 23, side walls 25 an end wall 27 and a short bottom wall 29 extending between the side walls 25 adjacent the end wall 27.

Mounted at one end of the sledge 22 is a support 28 on which is carried a specimen holder 30 (shown only in FIG. 1). The support 28 is vertically movable relative to the sledge, the vertical movement being guided by the engagement of a guide member 32 fixed to the support in a dove-tail groove in the end wall 27 of the sledge. The specimen holder 30 is arranged to hold a specimen, such as that shown at 36 in FIG. I, so that, as the sledge 22 is pushed manually by means of handle 38 along the rails 20, a layer is cut from the specimen 36 as it passes the blade 24. Mounted in the sledge is a ratchet and pawl mechanism indicated generally by reference numeral 40 (FIGS. 3 to which is actuated at the beginning of each cutting stroke, as described below, to raise the support 28, and so raise the specimen holder 30, by a preselected amount, so that the specimen holder is raised between cutting operations by an amount equal to the desired thickness of the layers to be cut from the specimen.

The ratchet and pawl mechanism 40 comprises a horizontally disposed ratchet wheel 42 fixed to the lower end of a vertical screw-threaded rod 44. The ratchet wheel 42 and rod 44 are mounted by means of a ball bearing, 46 on a bearing member 48 fixed to the bottom wall 29, the rod 44 and ratchet wheel 42 being held in position by a spring-biased screw 52. The threaded rod 44'engages a nut 54 pivotally mounted by stub axles 56 between two vertical side walls 58 of the specimen holder support 28. The nut 54 is pivotal between two positions, in one of which it engages the threads of the rod 54 and in the other of which it can move freely over the threaded rod, as described in US Pat. No. 3,757,591. When the nut 54 is in engagement with the and main lever 60, unless main lever 60 is positively held against rotation.

A trip assembly 86 (FIGS. 4 and 5) is mounted on the side wall 18 of base casting so as to engage the pro- 5 jecting end of the auxiliary lever 70 as the sledge 22 threads of rod 44, rotation of the rod by rotation of the ratchet wheel in the anti-clockwise direction as seen in FIGS. 5 and 7 causes the nut, and hence the support 28 and specimen holder 30, to be moved upwards by an amount proportional tothe angle through which the wheel is rotated.

Beneath the ratchet wheel 42 is a main lever 60 which is rotatably mounted on the bearing member 48, between the wall 29 and a flange 62 on member 48, so that the lever 60 is rotatable about the same vertical axis as the ratchet wheel. A pawl 64 is pivotally mounted at one end of the main lever 60 and is biased into engagement with the ratchet wheel 42 by means of a spring 66 (FIG. 4), so that rotation of the main lever 60 in the anti-clockwise direction as seen in FIGS. 5 and 7 causes rotation of the ratchet wheel in the same' direction. During movement of main lever 60 in the opposite direction pawl 64 rides over the teeth of ratchet wheel 42 which is held stationary during this movement by a second spring-loaded pawl 67, pivotally mounted on a lever 68 coaxial with main lever 60. Lever 68 is normally held stationary, but can be rotated through a preset angle by manual operation of lever 69 on the upper wall of the sledge, as described in US. Pat. No. 3,757,591, to enable the specimen holder to be raised in fixed steps during trimming of the microtome before beginning cutting operations.

At the end opposite the pawl 64, the main lever 60 carries an auxiliary lever 70 (FIGS. 4, 5 and 7), pivoted on pin 72 for rotation about a vertical axis, one end 76 of the auxiliary lever projecting beyond the end of the main lever. A tension spring 78 is connected between the other end of the auxiliary lever 70 and an anchorage 80 on the main lever 60, to bias the auxiliary lever to rotate relative to the main lever in the clockwise direction as seen in FIGS. 5 and 7. A stop 82 formed on the end of the auxiliary lever 70 engages one edge 84 of the main lever 60 to limit movement of the auxiliary lever by the spring 78. The spring modulus of tension spring 78 is sufficiently high to ensure that movement of the end 76 of auxiliary lever 70 in the opposite direction will effect rotation in the anti-clockwise direction of the main lever 60 and ratchet wheel 42 without appreciable relative rotation between auxiliary lever 70 moves towards knife 24 at the beginning of each cutting stroke. The trip assembly comprises a generally channel-shaped body 88 to which is fixed a screw 90 which projects through a horizontally extending slot 92 in the wall 88 and receives a clamping knob 94 by means of which body 88 is held in position. Upon loosening the clamping knob 94 the trip assembly can be moved along the slot 92 to adjust the point in the travel of the sledge at which the auxiliary lever strikes the trip assembly. A lever 96 is mounted at one end on the body 88 by means of a vertical pivot pin 98, and carries at its other end a trip pin 100, the lower end of which is normally positioned so as to engage the projecting end of auxiliary lever 70 during travel of the sledge. A tension spring 102, connected between the end of lever 96 adjacent pivot 98 and the base of a stud 104 fixed to the body 88, biases the lever 96 to its normal position in which it engages a stop formed by a nut 106 screwed onto the threaded end of stud 104, whilst allowing pivotal movement of the lever to move the pin out of engagement with auxiliary lever 70 at the ends of its travel. A guide member 109 (FIGS. 4 and 6) fixed to the sledge engages pin 100 to prevent pivotal movement of lever 96 during travel of the lever 70 in either direction.

The ends of the main lever 60 and auxiliary lever 70 project through an opening 108 in the adjacent side wall 25 of the sledge 22. Two plates forming stop members 110 and 112 are fixed to the side wall 25 at one end of the opening 108, by means of screws 114. Stop member 110 projects into opening 108 and is positioned to engage the main lever 60 to bring it to a halt at a predetermined point in the rotation of the lever caused by engagement of auxiliary lever 70 with the trip assembly 86. The other stop member 112 also projects into cavity 108 and is arranged to engage the auxiliary lever 70 at a point on the side of its pivot 72 opposite its projecting end 76, the main lever 60 moving above the stop member. The stop member 112 is positioned so that it engages the auxiliary lever 70, during rotation of the main lever 60, a few degrees before the stop member 110 engages the main lever 60.

The distance through which the specimen holder 30 is raised in each operation of the ratchet and pawl mechanism is adjustable by means of a mechanism ineluding a lever 116 mounted co-axially with ratchet wheel 42. Lever 116 has an arcuate cam surface 118 which is engaged by a follower 120 on pawl 64 to draw the pawl out of engagement with the ratchet wheel 42. Thus, during anti-clockwise rotation of main lever 60, pawl 64 moves into engagement with ratchet 42 only when the follower 120 reaches the end of cam surface 118. The angular position of the cam surface 116 can be varied by rotating knob 122 which rotates a pinion 124 engaging a rack 126 on the end of lever 116 and thereby rotates lever 116.

The microtome described includes a mechanism, actuated by lever 130, for tilting nut 54 out of engagement with threaded rod 44 so that support 28 can be raised or lowered rapidly by turning knob 132 which rotates, through gear assembly 134 and connecting rod 136, a pinion 138 engaging a rack 140 fixed to support 28. This mechanism is more fully described in US. Pat. No. 3,757,591.

In operation of the microtome, as the sledge 22 is moved towards the knife 24 at the beginning of a cutting stroke, the outer end of auxiliary lever 70 engages the pin 100 of the trip assembly as shown in FIG. 7A, causing the auxiliary lever 70 and main lever 60 to rotate at a speed dependent on the speed of movement of the sledge. When pawl 6d reaches the end of cam surface 118 it moves into engagement with ratchet wheel 42, which is therefore rotated with lever 60 to raise specimen holder 30. When auxiliary lever 70 engages stop member 112, the lever 70 is caused to rotate relative to the main lever 60 against the bias of spring 78, as shown diagrammatically in FIG. 7B. This movement continues until main lever 60 engages stop member 110 to halt rotation of the levers, whereupon the lever 70 moves past the trip assembly, as described above, and the sledge continues its movement to complete the cutting stroke. During the final part of the movement of levers 60 and 70, the projecting end 76 of lever 70 travels further than the adjacent end of lever 60, so that the angular velocity of the main lever till is reduced. If the sledge moves at constant speed, the angular velocity of lever 60 is reduced by a factor X/Y sin d), where, as shown in FIG. 78, X and Y are the distances, measured in a direction perpendicular to the direction of travel of the sledge, between the pivotal axis 72 of lever 76 and, respectively, the trip pin 100 and the point of engagement of stop member 112 with lever 70, and is the angle between the line joining pivotal axis 72 to the point of contact of lever 70 with pin 100 and the direction of travel of the sledge. The speed of rotation of the ratchet wheel 42 is therefore reduced over the last few degrees of its travel, and the danger of the wheel overrunning is reduced.

I claim:

1. A microtome of the kind set forth, in which the ratchet and pawl mechanism comprises a ratchet wheel rotatably mounted on one of the relatively movable members and arranged so that rotation of the ratchet wheel in one sense through a pre-set angle effects a correspondingly pre-set decrease in the separation between the knife and specimen holder, a lever assembly pivotally mounted on the same member and carrying a pawl which engages the ratchet wheel during pivotal movement of the lever assembly in one sense to effect rotation in the said sense of the ratchet wheel, a trip element mounted on the other of the relatively movable members so as to engage the lever assembly during relative movement of the members in one direction thereby to cause rotation of the lever assembly in the said sense, a stop element mounted on the firstmentioned one of the relatively movable members and positioned to engage the lever assembly to stop, at a predetermined point, rotation thereof by the trip element, the lever assembly including means for reducing, during part of the rotation of the lever assembly immediately before its engagement with the stop element, the speed of rotation of the ratchet wheel effected by a given speed of relative movement between the relatively movable members.

2. A microtome as claimed in claim l, in which the lever assembly comprises a main lever carrying the pawl, and an auxiliary lever pivotally mounted on the main lever for rotation about an axis parallel to and spaced from the pivotal axis of the main lever and posi tioned so as to be engaged by the trip element, at a point on one side of its pivotal axis, resilient biasing means connected between the main and auxiliary levers to urge the main lever to follow the rotation of the auxiliary lever when it is engaged by the trip element, and a second stop element positioned to engage the auxiliary lever, at a point on the side of its pivot axis opposite its point of contact with the trip element, before the main lever engages the first-mentioned stop element, so that, during part of the rotation of the lever assembly immediately before engagement of the main lever with the first stop element, the auxiliary lever r0 tates relative to the main lever against the resilience of the biasing means thereby to reduce the speed of rotation of the main lever effected by a given speed of relative movement between the relatively movable members.

3. A microtome as claimed in claim 2, in which the pawl and the auxiliary lever are mounted at respective ends of the main lever on opposite sides of the axis of rotation of the main lever, and the auxiliary lever is positioned to be engaged by the trip element at a point on the side of the pivotal axis of the auxiliary lever remote from the pivotal axis of the main lever.

4. A microtome as claimed in claim 2, in which the resilient biasing means comprises a tension spring connected between one end of the auxiliary lever and a point on the main lever.

5. A microtome as claimed in claim 1, in which the relatively movable members comprise a base and a sledge supported by and linearly movable on the base, the base being adapted to support the knife in a fixed position, the ratchet and pawl mechanism being mounted in the sledge and operable to move the specimen holder supported by the sledge, and the trip element being mounted on the base so as to be engaged by the lever assembly of the ratchet and pawl mechanism during linear movement of the sledge.

6. A microtome as claimed in claim 3, in which the resilient biasing meanscomprises a tension spring con nected between one end of the auxiliary lever and a point on the main lever.

7. A microtome as claimed in claim 2, in which the relatively movable members comprise a base and a sledge supported by and linearly movable on the base, the base being adapted to support the knife in a fixed position, the ratchet and pawl mechanism being mounted in the sledge and operable to move the specimen holder supported by the sledge, and the trip element being mounted on the base so as to be engaged by the lever assembly of the ratchet and pawl mechanism during linear movement of the sledge.

8. A microtome as claimed in claim 3 in which the relatively movable members comprise a base and a sledge supported by and linearly movable on the base, the base being adapted to support. the knife in a fixed position, the ratchet and pawl mechanism being mounted in the sledge and operable to move the specimen holder supported by the sledge, and the trip element being mounted on the base so as to be engaged by the lever assembly of the ratchet and pawl mechanism during linear movement of the sledge.

9. A microtome as claimed in claim 4 in which the relatively movable members comprise a base and a sledge supported by and linearly movable on the base, the base being adapted to support the knife in a fixed position, the ratchet and pawl mechanism being the base being adapted to support the knife in a fixed position, the ratchet and pawl mechanism being mounted in the sledge and operable to move the specimen holder supported by the sledge, and the trip element being mounted on the base so as to be engaged by the lever assembly of the ratchet and pawl mechanism during linear movement of the sledge. 

1. A microtome of the kind set forth, in which the ratchet and pawl mechanism comprises a ratchet wheel rotatably mounted on one of the relatively movable members and arranged so that rotation of the ratchet wheel in one sense through a pre-set angle effects a correspondingly pre-set decrease in the separation between the knife and specimen holder, a lever assembly pivotally mounted on the same member and carrying a pawl which engages the ratchet wheel during pivotal movement of the lever assembly in one sense to effect rotation in the said sense of the ratchet wheel, a trip element mounted on the other of the relatively movable members so as to engage the lever assembly during relative movement of the members in one direction thereby to cause rotation of the lever assembly in the said sense, a stop element mounted on the firstmentioned one of the relatively movable members and positioned to engage the lever assembly to stop, at a predetermined point, rotation thereof by the trip element, the lever assembly including means for reducing, during part of the rotation of the lever assembly immediately before its engagement with the stop element, the speed of rotation of the ratchet wheel effected by a given speed of relative movement between the relatively movable members.
 2. A microtome as claimed in claim 1, in which the lever assembly comprises a main lever carrying the pawl, and an auxiliary lever pivotally mounted on the main lever for rotation about an axis parallel to and spaced from the pivotal axis of the main lever and positioned so as to be engaged by the trip element, at a point on one side of its pivotal axis, resilient biasing means connected between the main and auxiliary levers to urge the main lever to follow the rotation of the auxiliary lever when it is engaged by the trip element, and a second stop element positioned to engage the auxiliary lever, at a point on the side of its pivot axis opposite its point of contact with the trip element, before the main lever engages the first-mentioned stop element, so that, during part of the rotation of the lever assembly immediately before engagement of the main lever with the first stop element, the auxiliary lever rotates relative to the main lever against the resilience of the biasing means thereby to reduce the speed of rotation of the main lever effected by a given speed of relative movement between the relatively movable members.
 3. A microtome as claimed in claim 2, in which the pawl and the auxiliary lever are mounted at respective ends of the main lever on opposite sides of the axis of rotation of the main lever, and the auxiliary lever is positioned to be engaged by the trip element at a point on the side of the pivotal axis of the auxiliary lever remote from the pivotal axis of the main lever.
 4. A microtome as claimed in claim 2, in which the resilient biasing means comprises a tension spring connected between one end of the auxiliary lever and a point on the main lever.
 5. A microtome as claimed in claim 1, in which the relatively movable members comprise a base anD a sledge supported by and linearly movable on the base, the base being adapted to support the knife in a fixed position, the ratchet and pawl mechanism being mounted in the sledge and operable to move the specimen holder supported by the sledge, and the trip element being mounted on the base so as to be engaged by the lever assembly of the ratchet and pawl mechanism during linear movement of the sledge.
 6. A microtome as claimed in claim 3, in which the resilient biasing means comprises a tension spring connected between one end of the auxiliary lever and a point on the main lever.
 7. A microtome as claimed in claim 2, in which the relatively movable members comprise a base and a sledge supported by and linearly movable on the base, the base being adapted to support the knife in a fixed position, the ratchet and pawl mechanism being mounted in the sledge and operable to move the specimen holder supported by the sledge, and the trip element being mounted on the base so as to be engaged by the lever assembly of the ratchet and pawl mechanism during linear movement of the sledge.
 8. A microtome as claimed in claim 3 in which the relatively movable members comprise a base and a sledge supported by and linearly movable on the base, the base being adapted to support the knife in a fixed position, the ratchet and pawl mechanism being mounted in the sledge and operable to move the specimen holder supported by the sledge, and the trip element being mounted on the base so as to be engaged by the lever assembly of the ratchet and pawl mechanism during linear movement of the sledge.
 9. A microtome as claimed in claim 4 in which the relatively movable members comprise a base and a sledge supported by and linearly movable on the base, the base being adapted to support the knife in a fixed position, the ratchet and pawl mechanism being mounted in the sledge and operable to move the specimen holder supported by the sledge, and the trip element being mounted on the base so as to be engaged by the lever assembly of the ratchet and pawl mechanism during linear movement of the sledge.
 10. A microtome as claimed in claim 6 in which the relatively movable members comprise a base and a sledge supported by and linearly movable on the base, the base being adapted to support the knife in a fixed position, the ratchet and pawl mechanism being mounted in the sledge and operable to move the specimen holder supported by the sledge, and the trip element being mounted on the base so as to be engaged by the lever assembly of the ratchet and pawl mechanism during linear movement of the sledge. 